As one example of a construction vehicle, a wheel loader will be cited and explained. As shown in FIGS. 1(a) through 1(c), a wheel loader 100 comprises a main body 102 that has propulsion wheels 104, and a working equipment 106 that is attached to this main body 102. The working equipment 106 comprises a boom 108, a bucket 110, a boom cylinder (omitted from the figure), a bucket cylinder 112, and so on.
This wheel loader 100 performs an excavation task in which it loads broken store or earth and sand into the bucket 110, by pushing the bucket 110 forward into a heap of broken stone or earth and sand after blasting while driving the vehicle body forward. Moreover, when excavating a vertical wall such as a cliff face or the outer wall of a building, normally, as shown in FIGS. 1(a) through 1(c), the bucket 110 is pushed against the wall and digs into the wall due to a strong forward propelling force from the propulsion wheels 104.
A technique is known for preventing slippage of the propulsion wheels when performing this type of task, by detecting symptoms of slippage, and by adjusting the amount of engagement of a modulation clutch or adjusting the fuel injection amount of the engine (for example, refer to Patent Documents #1 and #2).